Wow, my new user registration page looks incomprehensibly bad! (how to fix?)

So I finally got up enough nerve to turn on the comment system (after installing the Comment Spam Pack). So far, so good. But it turns out the new user registration page is ungodly ugly.

How can I fix this?

The site I want to allow comments on is

The main WordPress site that hosts all the blogs is (with a temporary theme).

And below is an example of just how fugly that signup page is. So, tips for making it at least tolerable would be much appreciated.